A display apparatus is an electric optical apparatus converting an electric signal into an optical image so that a user recognizes information. A liquid crystal display (hereinafter, referred to as LCD) apparatus of the display apparatus supplies electrical field to transform an arrangement of liquid crystal molecules by means of an optical characteristics of the liquid crystal.
A TFT of a large display substrate needs a low gate resistance to prevent signal delay and flickering of an image. Metals such as copper or aluminum have low resistance and high conductivity. However, the metals are improper for manufacturing an LCD apparatus. The copper has the lowest resistivity among the metals, but the copper has low adhesiveness to a silicon-containing substrate. The copper is also oxidized easily. The copper may be prevented from diffusing into the silicon containing substrate, and sufficient adhesiveness may be necessary so as to use the copper wiring in the TFT process.
The diffusion of the copper into the silicon-containing substrate deteriorates ohmic contact characteristics of elements, and the low adhesiveness causes lift-off of a thin film and abrasion of the thin film. The lift-off and the abrasion cause problems in manufacturing process.